Ad-hoc wireless communication networks designed for stations with high mobility, e.g. vehicular ad-hoc networks (VANETs), require that each station has reliable and up-to-date information of its neighbourhood topology. In VANETs the neighbourhood information is advantageous, for instance, to cooperative driving and danger warning applications, as well as to packet routing and channel access coordination. To derive the neighbour topology information, stations in the communication range have to periodically exchange information with each other. A way of exchanging information is to use a beacon message, which broadcasts the information of the sender to its neighbouring stations. By receiving the beacons from the neighbours, a station can derive the current network topology in its vicinity. An efficient way of exchanging beacons is to use a specifically defined synchronised beacon period.
Beacon collision happens if at least two stations that are within a communication range choose the same beacon slot for transmission of a beacon signal. The probability of a beacon collision depends on the number of stations in the communication range and the total number of beacon slots available. However, in scenarios where the number of stations in the same communication range is large and the number of available beacon slots is limited, the beacon collision probability is relatively high. Also the time needed to solve a beacon collision may be longer.
The problem of having long beacon collision resolution time is more critical in wireless communication networks with high station mobility. This is due to high mobility which introduces more frequent topology changes and beacon collisions. In order to have a relatively stable network structure, the beacon collisions have to be solved rapidly.
Distributed wireless networks may be organised without a central coordinator. In these kinds of networks, like the WiMedia/multiband OFDMA alliance (MBOA) systems, stations transmit their beacons for coordinating the channel access and getting the neighbourhood information. The beacons are transmitted periodically in the synchronised interval, and a specifically designed beacon period consisting of multiple of beacon slots is used for beacon transmission in each interval.
United States patent application publication 2005/0226203 discloses a method, where a primary beacon is transmitted specifying an order at which other nodes are to transmit secondary beacons. The secondary beacons are then transmitted at the time specified in the primary beacon. Preferably, the secondary beacons comprise the same, or at least substantially the same, wireless access information as the primary beacon.
Thus, there is a need for an improved method of reducing beacon collision probability in communication systems.